Hi there,
This is Bogdan from Romania.
I'm a mechanical engineer - specialized in the industrial robotic field, 3D designer, industrial designer and, 3D modeler.
For some of my projects, I'm also doing the physical prototype too.
I'm doing product design, industrial design, reverse engineering, ideation, etc.
I have over 15 years of experience working on various systems/devices across multiple industries, from concept to launch.
Downloaded and checked the model - it is clear what is wrong with the model, but unfortunately a stl file can't be edited (will need conversion to another parametric cad format, and after this to be edited)
The best solution is to rebuild it from scratch following the proper techniques and limitations.
Another good point, is to have the model divided into several parts (better for 3d printing, shipping, and also may be fun for kids to paint and assemble :) )
For any more questions, we could chat here, including the whole details of the project, final price, time frame, deliverables, etc, etc...
Regards
Bogdan